Rubber-modified resin and thermoplastic resin composition containing the same

ABSTRACT

A rubber-modified resin obtained by conducting polymerization of a vinyl monomer in the presence of a mixed rubber latex of a silicone rubber latex (A) and an acrylic rubber latex (B), during which polymer particles are coagglomerated to enhance the particle size. The rubber-modified resin is useful as impact modifier and provides thermoplastic resin compositions having an excellent impact resistance by the incorporation thereof into thermoplastic resins.

RELATED APPLICATIONS

This application is a nationalization of PCT application PCT/JP01/10465filed Nov. 30, 2001. This application claims priority from the PCTapplication and Japan Application Ser. No. 2000-370273 filed Dec. 5,2000.

TECHNICAL FIELD

The present invention relates to a rubber-modified resin useful as animpact modifier for thermoplastic resins, and a thermoplastic resincomposition containing the same. More particularly, the presentinvention relates to a rubber-modified resin wherein a resin is modifiedwith two rubbers of a silicone rubber and an acrylic rubber, and athermoplastic resin composition having an excellent impact resistance.

BACKGROUND ART

It has been popularly practiced to improve the impact resistance ofthermoplastic resins by incorporating a rubber-modified resin containinga rubber component into the thermoplastic resins.

It has been considered advantageous in exhibiting impact resistance touse a rubber component having a glass transition temperature (Tg) as lowas possible. In practice, a resin composition incorporated with a resinmodified with a polybutadiene-based rubber having a low Tg of about −80°C., e.g., acrylonitrile/butadiene/styrene copolymer (ABS resin), has ahigher impact resistance than a resin composition incorporated with aresin modified with a polybutyl acrylate rubber having a Tg of about−50° C.

In respect of low Tg of rubbers, a polyorganosiloxane rubber(hereinafter also referred to as “silicone rubber”) can be expected toimpart a higher impact resistance as compared with rubber-modifiedresins containing a polybutadiene-based rubber component ifrubber-modified resins containing a silicone rubber can be utilized asimpact modifier, since for example the Tg of polydimethylsiloxane rubberis about −120° C.

Use of silicone rubber is also advantageous from the viewpoint ofweatherability as being superior to polybutyl acryalate rubber andpolybutadiene-based rubber.

From such a point of view, recently, it has been variously investigatedto use resins modified with silicone rubber or composite rubberscontaining silicone rubber as an impact modifier for thermoplasticresins. For example, JP-A-4-100812 discloses using a graft copolymerprepared by graft-polymerizing a vinyl monomer onto a composite rubberwherein a silicone rubber component and a polyalkyl (meth)acrylatecomponent are unseparably entangled with each other. Also,JP-A-11-100481 discloses using a graft copolymer prepared byco-agglomerating silicone rubber particles and acrylic rubber particlesto give a composite rubber of enhanced particle size andgraft-polymerizing a vinyl monomer onto the composite rubber.

The impact resistance of thermoplastic resins is further improved byincorporation of, as an impact modifier, these graft copolymers preparedusing the composite rubbers as mentioned above in compared with singleuse of conventional rubbers such as polybutadiene-based rubber andacrylic rubber. However, the degree of improvement is not so large asone expects.

It is an object of the present invention to provide an impact modifierhaving a remarkably improved effect of imparting impact resistance.

A further object of the present invention is to provide a thermoplasticresin composition having an improved impact resistance.

DISCLOSURE OF INVENTION

The present inventors have found that a rubber-modified resin having aremarkably improved impact resistance-imparting effect can be preparedby polymerizing a vinyl monomer in the presence of a mixed rubber latexof a silicone rubber latex and an acrylic rubber latex and, during thepolymerization, coagglomerating polymer particles present in the mixedlatex to enhance the particle size.

Thus, the present invention provides a rubber-modified resin obtained bypolymerizing a vinyl monomer in the presence of (A) a silicone rubberlatex and (B) an acrylic rubber latex and, during the polymerization,coagglomerating polymer particles to enhance the particle size.

The rubber-modified resin of the present invention contains a siliconerubber and an acrylic rubber as the rubber component. The siliconerubber used in the present invention comprehends a polyorganosiloxaneand a modified polyorganosiloxane wherein a polyorganosiloxane is partlyreplaced with an organic polymer having no polyorganosiloxane segment.It is preferable that the amount of silicone (polyorganosiloxane) in thetotal rubber component of the modified-rubber resin is from 1 to 90% byweight based on 100% by weight of the total of the silicone rubber andthe acrylic rubber. Also, it is preferable that the amount of the totalrubber latex is from 40 to 98 parts by weight (solid basis) and theamount of the vinyl monomer is from 2 to 60 parts by weight,respectively, based on 100 parts by weight of the total of the wholerubber component and the vinyl monomer. Preferably the particle sizeenhancement by coagglomeration is conducted by adding an electrolyte tothe polymerization system on or before the polymerization conversion ofthe vinyl monomer reaches 90% by weight, especially when thepolymerization conversion reaches 10 to 70% by weight.

The rubber-modified resin of the present invention can be incorporatedinto various thermoplastic resins, whereby the impact resistance of thethermoplastic resins is remarkably improved.

Thus, the present invention also provides a thermoplastic resincomposition comprising a thermoplastic resin and 0.1 to 150 parts byweight of the above-mentioned rubber-modified resin per 100 parts byweight of the thermoplastic resin.

BEST MODE FOR CARRYING OUT THE INVENTION

The rubber-modified resins of the present invention are those preparedby polymerizing a vinyl monomer in the presence of a mixed rubber latexof (A) a silicone rubber latex and (B) an acrylic rubber latex and,during the polymerization, coagglomerating polymer particles in thelatex to enhance the particle size. That is to say, the rubber-modifiedresins comprise particles formed by particle size-enhancingco-agglomeration, which is conducted in the course of the graftpolymerization, of graft copolymer particles wherein a vinyl monomer isgraft-polymerized onto a silicone rubber (or particles wherein thesilicone rubber and a polymer of the vinyl monomer are physicallycoexist if the silicone rubber has no grafting site) and graft copolymerparticles wherein the vinyl monomer is graft-polymerized onto an acrylicrubber (or particles wherein the acrylic rubber and the vinyl polymerare physically coexist if the acrylic rubber has no grafting site).

The rubber-modified resins of the present invention have the advantageof being superior in impact resistance-imparting effect as compared witha rubber-modified resin prepared in the same manner as the presentinvention but without conducting the particle size enhancingcoagglomeration during the polymerization of vinyl monomer, and arubber-modified resin prepared in such a manner as coagglomerating alatex of a mixed rubber (silicone rubber and acrylic rubber) prior tothe polymerization of vinyl monomer, namely a graft copolymer preparedby graft-polymerizing a vinyl monomer onto a composite rubber ofsilicone rubber and acrylic rubber.

The term “silicone rubber” as used herein comprehends apolyorganosiloxane having rubber elasticity, namely a conventionalsilicone rubber, a modified silicone rubber composed of a siliconerubber and an organic polymer having no silicone (polyorganosiloxane)segment (e.g., butyl acrylate polymer rubber, butadiene polymer rubber,styrene polymer, styrene-butyl acrylate copolymer, styrene-acrylonitrilecopolymer or methyl methacrylate polymer), and the like. The modifiedsilicone rubber includes a modified silicone rubber wherein a siliconerubber and an organic polymer having no silicone segment are chemicallybonded, a modified silicone rubber wherein a silicone rubber and anorganic polymer having no silicone segment are entangled, and a modifiedsilicone rubber wherein a silicone rubber and an organic polymer havingno silicone segment merely coexist without entangling each other.

The term “acrylic rubber” as used herein means a rubber (elastomer)containing at least 50% by weight, especially at least 60% by weight, ofunits of a (meth)acrylic monomer.

From the viewpoint of easiness in particle size enhancement bycoagglomeration operation mentioned after, it is preferable that thesilicone rubber particles included in the silicone rubber latex (A) havean average particle size of 10 to 200 nm, especially 20 to 150 nm.

The content of solvent-insoluble matter in the silicone rubberparticles, namely the gel content of the silicone rubber, denotes aweight percentage of a toluene-insoluble matter measured by immersing asample in toluene at room temperature for 24 hours and centrifuging at12,000 rpm for 1 hour. It is also preferable from the viewpoint ofexhibiting impact strength that the content of solvent-insoluble matterin the silicone rubber particles is from 0 to 100% by weight, especially40 to 100% by weight.

The content of silicone (polyorganosiloxane) component included in thesilicone rubber particles is not particularly limited, but is preferablyat least 50% by weight, especially at least 60% by weight, from theviewpoint of exhibiting impact resistance. The maximum value thereof is100% by weight.

Examples of the silicone rubber are, for instance, dimethylsiloxanerubber, a modified silicone rubber composed of butyl acrylate rubber anddimethylsiloxane rubber which are chemically bonded, a modified siliconerubber composed of butyl acrylate rubber and dimethylsiloxane rubberwhich are entangled with each other, a modified silicone rubber composedof butyl acrylate rubber and dimethylsiloxane rubber which merelycoexist without being entangled with each other, a modified siliconerubber composed of styrene-butyl acrylate copolymer and dimethylsiloxanerubber which are chemically bonded, a modified silicone rubber composedof styrene-butyl acrylate copolymer and dimethylsiloxane rubber whichare entangled with each other, a modified silicone rubber composed ofstyrene-butyl acrylate copolymer and dimethylsiloxane rubber whichmerely coexist without being entangled with each other, and the like.

The silicone rubber latex (A) used in the present invention usually hasa solid concentration of 10 to 50% by weight (measured after drying at120° C. for 1 hour). Silicone rubber latex (A) having a solidconcentration of 20 to 40% by weight is preferred from the viewpoint ofeasiness in controlling the particle size by the particle sizeenhancement operation mentioned after.

The silicone rubber latex (A) is prepared, for instance, by emulsionpolymerization using, as a main component, a silicone rubber-formingcomponent comprising an organosiloxane (a) and optionally a crosslinkingagent (b), a graftlinking agent (c) and other organosilane (d) thanthose used as the crosslinking agent and the graftlinking agent.

The organosiloxane (a) is a component which constitutes the backbone ofthe silicone rubber chains, and linear and cyclic organosiloxanes can beused. Cyclic organosiloxanes are preferred from the viewpoints ofapplicability to emulsion polymerization system and economy. Examples ofthe cyclic organosiloxane are, for instance, hexamethylcyclotrisiloxane(D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane(D5), dedecamethylcyclohexasiloxane (D6),tetradecamethylcycloheptasiloxane (D7), hexadecamethyl-cyclooctasiloxane(D8), and the like. The organosiloxanes may be used alone or inadmixture thereof. In particular, D4, a mixture of D3 to D7 and amixture of D3 to D8 are preferably used from an economical point ofview.

The crosslinking agent (b) is optionally used for the purpose ofintroducing a crosslinked structure into the silicone rubber bycopolymerization with the organosiloxane (a), thereby imparting a rubberelasticity to the silicone rubber. Examples thereof are, for instance,tetrafunctional and trifunctional alkoxysilane compounds such astetramethoxysilane, tetraethoxysilane, triethoxymethylsilane,triethoxyethylsilane, butyltrimethoxysilane, butyltriethoxysilane,propyltrimethoxysilane and octyltrimethoxysilane, and othertetrafunctional and trifunctional silane compounds. These may be usedalone or in admixture thereof. Of these, alkoxysilane compounds having aC₂ to C₈ monovalent hydrocarbon group are preferred from the viewpointsof imparting an affinity with acrylic rubber component to the obtainedsilicone rubber to thereby controlling the impact resistance-impartingeffect.

The graftlinking agent (c) includes reactive silane compounds having apolymerizable unsaturated bond or a mercapto group in their molecules.It is optionally used for the purpose of introducing polymerizableunsaturated bonds or mercapto group into the side chains or molecularchain ends of copolymers by the copolymerization with the organosiloxaneand optionally the crosslinking agent and the like. The polymerizableunsaturated bond or mercapto group serves as an active site for graftingof vinyl monomers mentioned after. The polymerizable unsaturated bond ormercapto group also serves as a crosslinking point which formscrosslinkages by a radical reaction between them through a radicalpolymerization initiator. Even in the case that crosslinking isconducted by radical reaction, a part of the unsaturated bonds ormercapto groups remain as a grafting point and, therefore, grafting ispossible.

Examples of the reactive silane compound having a polymerizableunsaturated bond in its molecule are, for instance, a silane compound ofthe formula (1):

wherein R¹ is hydrogen atom or methyl group, R² is a monovalenthydrocarbon group having 1 to 6 carbon atoms, X is an alkoxyl grouphaving 1 to 6 carbon atoms, a is 0, 1 or 2, and p is an integer of 1 to6, a silane compound of the formula (2):

wherein R², X, a and p are as defined above, a silane compound of theformula (3):

wherein R², X and a are as defined above, a silane compound of theformula (4):

wherein R², X and a are as defined above, and R³ is a bivalenthydrocarbon group having 1 to 6 carbon atoms, and the like.

Examples of the group R² in the formulas (1) to (4) are, for instance,an alkyl group such as methyl group, ethyl group or propyl group, phenylgroup, and the like. Examples of the group X are, for instance, analkoxyl group having 1 to 6 carbon atoms such as methoxy group, ethoxygroup, propoxy group or butoxy group, and the like. Examples of thegroup R³ in the formula (4) are, for instance, methylene group, ethylenegroup, trimethylene group, tetramethylene group, and the like.

Examples of the reactive silane compound (1) are, for instance,β-methacryloyloxyethyldimethoxymethylsilane,γ-methacryloyloxy-propyldimethoxymethylsilane,γ-methacryloyloxypropyltrimethoxysilane,γ-methacryloyloxypropyldimethylmethoxysilane,γ-methacryloyloxypropyltriethoxysilane,γ-methacryloyloxypropyldiethoxymethylsilane,γ-methacryloyloxypropyltripropoxysilane,γ-methacryloyloxypropyldipropoxymethylsilane,γ-acryloyloxypropyldimethoxymethylsilaneγ-acryloyloxypropyltrimethoxysilane, and the like. Examples of thereactive silane compound (2) are, for instance,p-vinylphenyldimethoxymethylsilane, p-vinylphenyltrimethoxysilane,p-vinylphenyltriethoxysilane, p-vinylphenyldiethoxymethylsilane, and thelike. Examples of the reactive silane compound (3) are, for instance,vinylmethyldimethoxysilane, vinylmethyldiethoxysilane,vinyltrimethoxysilane, vinyltriethoxysilane, and the like. Examples ofthe reactive silane compound (4) are, for instance,allylmethyldimethoxysilane, allylmethyldiethoxysilane,allyltrimethoxysilane, allyltriethoxysilane, and the like. Of these,silane compounds of the formulas (1) and (3) are preferably used fromthe viewpoints of economy and reactivity.

A typical example of the reactive silane compound having mercapto groupin its molecule is a silane compound of the formula (5):

wherein R², X and a are as defined above, and R⁴ is a bivalent organicgroup such as an alkylene group having 1 to 18 carbon atoms. Examples ofthe alkylene group are, for instance, methylene group, ethylene group,trimethylene group, tetramethylene group and the like.

Examples of the reactive silane compound (5) are, for instance,mercaptopropyltrimethoxysilane, mercaptopropyldimethoxymethylsilane, andthe like.

Reactive silane compounds of trialkoxysilane type serve both as agraftlinking agent and as a crosslinking agent.

The organosilanes (d) other than the above-mentioned crosslinking agent(b) and graftlinking agent (c) serve to impart an affinity with anacrylic rubber to the obtained silicone rubbers. They include, forinstance, organosilane compounds having a structural unit of the formula(6):

wherein R⁵ and R⁶ are a monovalent hydrocarbon group having 1 to 10carbon atoms, e.g., methyl group, ethyl group, propyl group or phenylgroup, and R⁵ and R⁶ may be the same or different unless they aresimultaneously methyl group. Examples of the organosilane having thestructural unit (6) are, for instance, methylbutyldimethoxysilane,dibutyldimethoxysilane, methyloctyldimethoxysilane,phenylmethyldimethoxysilane, diphenyldimethoxysilane and otherdialkoxysilane compounds. These may be used alone or in admixturethereof. If the organosiloxane (a), crosslinking agent (b) orgraftlinking agent (c) has the structural unit of the formula (6), thereis no need to use the other organosilane (d).

With respect to the proportions of the organosiloxane (a), crosslinkingagent (b), graftlinking agent (c) and other organosilane (d) in thesilicone rubber-forming component, it is preferable that the proportionof the organosiloxane (a) is from 59.9 to 99.9% by weight, especially 70to 99% by weight, the proportion of the crosslinking agent (b) is from 0to 40% by weight, especially 0.5 to 20% by weight, the proportion of thegraftlinking agent (c) is from 0 to 40% by weight, especially 0.5 to 20%by weight, and the proportion of the other organosilane (d) is from 0 to40% by weight, especially 0 to 29% by weight (the total of (a) to (d) is100% by weight). The crosslinking agent and the graftlinking agent areoptional components, but it is preferable that the amounts of thecrosslinking agent and the graftlinking agent are not simultaneously 0%by weight and either of them is used in an amount of at least 0.1% byweight. If the proportion of the organosiloxane is too small, theproduct lacks properties as a rubber, so the impact resistance-impartingeffect is decreased. If the proportion of organosiloxane is too large,the amounts of the crosslinking agent, graftlinking agent and otherorganosilane become to small, so the effects produced by the use thereoftend to be exhibit with difficulty. Also, if the proportion of thecrosslinking agent or graftlinking agent is too small, the impactresistance-imparting effect is small, and if the proportion is toolarge, the product lacks rubber-like properties, so the impactresistance-imparting effect also tends to be lowered. The otherorganosilane (d) is an optional component. An affinity with acrylicrubber component is provided by the use thereof, whereby the impactresistance-imparting effect can be adjusted. However, it is preferableto use the other organosilane (d) under consideration of balance betweenthe cost and the physical properties, since the use thereof leads toincrease in cost.

The silicone rubber latex (A) can be prepared, for example, by a methodwherein the silicone rubber-forming component comprising theorganosiloxane and optionally the crosslinking agent and thegraftlinking agent and further optionally the other organosilane isemulsified and dispersed into water by mechanical shearing in thepresence of an emulsifier and is polymerized under acidic condition. Incase of preparing modified silicone rubbers, the silicone rubber-formingcomponent is used in combination with a vinyl monomer component. In casethat emulsified droplets having a size of not less than severalmicrometers have been formed by mechanical shearing, it is possible tocontrol the average particle size of the silicone rubber particlesobtained after the polymerization within the range of 20 to 400 nmdepending on the amount of an emulsifier used. It is also possible toobtain the particles whose variation coefficient (100× standarddeviation/average particle size) (%) in the particle size distributionthereof is not more than 70%.

Also, when it is desired to prepare a silicone rubber having an averageparticle size of not more than 100 nm and a narrow particle sizedistribution, it is preferable to carry out the polymerization inmultistages. For example, 1 to 20% by weight of an emulsion comprisingemulsified droplets of not less than several micrometers obtained byemulsifying the silicone rubber-forming component, water and anemulsifier by means of mechanical shearing thereof is previouslysubjected to emulsion polymerization under an acidic condition, and theremaining emulsion is then added and polymerized in the presence of theproduced silicone rubber as seeds. In case of preparing the siliconerubber in such a manner, it is possible to control the average particlesize within the range of 20 to 100 nm depending on the amount of anemulsifier used, and also to control the variation coefficient in theparticle size distribution to not more than 60%. More preferable is amultistage polymerization method wherein a vinyl (co)polymer prepared byhomo- or copolymerizing a vinyl monomer, e.g., a vinyl monomer as usedin the graft polymerization mentioned after (such as styrene, butylacrylate or methyl acrylate) in a usual emulsion polymerization manneris used as seeds instead of the silicone rubber seeds in the abovemultistage polymerization, and a multistage polymerization is carriedout in the same manner as above. According to such a method, it ispossible to control the average particle size of the obtained siliconerubber (modified silicone rubber) within the range of 10 to 100 nm andthe variation coefficient in the particle size distribution to not morethan 50% depending on the amount of an emulsifier used.

The emulsion droplets of not less than several micrometers can beprepared by using a high speed agitating machine such as a homogenizer.

In these methods are used emulsifiers which do not lose an ability asemulsifier even under an acidic condition. Examples of such emulsifiersare, for instance, alkylbenzenesulfonic acid, sodiumalkylbenzenesulfonate, alkylsulfonic acid, sodium alkylsulfonate, sodium(di)alkyl sulfosuccinate, sodium polyoxyethylene nonylphenyl ethersulfonate, sodium alkylsulfate, and the like. These may be used alone orin admixture thereof.

Preferably the acidic condition is adjusted to a pH of 1 to 3 by addingan inorganic acid such as sulfuric acid or hydrochloric acid or anorganic acid such as alkylbenzenesulfonic acid, alkylsulfonic acid ortrifluoroacetic acid to the polymerization system, since the rate ofpolymerization is adequate.

The polymerization temperature to form the silicone rubber is preferablyfrom 60 to 120° C., more preferably from 70 to 100° C., since the rateof polymerization is adequate.

The silicone rubber latex is obtained in such a manner, but under anacidic condition the Si—O—Si bonds which constitute the backbone ofsilicone rubber are in an equilibrium state between severance andformation, and this equilibrium varies depending on the temperature.Accordingly, for the purpose of stabilization of silicone rubber chains,it is preferable to neutralize the latex by addition of an aqueoussolution of an alkali such as sodium hydroxide, potassium hydroxide orsodium carbonate. The equilibrium shifts to the formation side as thetemperature lowers and, therefore, a silicone rubber having a highmolecular weight or a high degree of crosslinking is easy to beproduced. Thus, when it is desired to obtain a silicone rubber having ahigh molecular weight or a high degree of crosslinking, it is preferablethat after conducting the polymerization for the production of siliconerubbers at a temperature of 60° C. or higher, the reaction mixture iscooled to room temperature or in the vicinity thereof, maintained atthat temperature for about 5 to about 100 hours and then neutralized.

Acrylic rubber latex (B) used in the present invention is, as mentionedabove, a latex of an acrylic rubber containing 50 to 100% by weight ofunits of a (meth)acrylic monomer. Any acrylic rubbers can be usedwithout particular restriction so long as they have properties as arubber. Examples thereof are, for instance, a latex of poly(butylacrylate) rubber, a latex of poly(2-ethylhexyl acrylate) rubber, a latexof butyl acrylate-2-ethyl hexyl acrylate copolymer rubber, a latex of acomposite rubber of poly(butyl acrylate) and poly(2-ethylhexylacrylate), and the like.

The acrylic rubber latex (B) usually has a solid concentration of 10 to50% by weight (measured after drying at 120° C. for 1 hour). Acrylicrubber latex (B) having a solid concentration of 20 to 40% by weight ispreferred from the viewpoint of easiness in controlling the particlesize by the particle size enhancement operation mentioned after.

From the viewpoint of easiness in particle size enhancement bycoagglomeration operation mentioned after, it is preferable that therubber particles included in the acrylic rubber latex (B) have anaverage particle size of 10 to 200 nm, especially 20 to 150 nm.

From the viewpoint of exhibiting impact strength, it is preferable thatthe content of solvent-insoluble matter in the rubber particles of theacrylic rubber latex (B) (gel content: weight fraction of atoluene-insoluble matter measured by immersing a sample in toluene atroom temperature for 24 hours and centrifuging at 12,000 rpm for 1 hour)is not less than 70% by weight, especially not less than 80% by weight.The maximum gel fraction is 100% by weight.

Examples of the acrylic rubber are, for instance, polybutyl acrylaterubber, butyl acrylate-2-ethylhexyl (meth)acrylate copolymer rubber, acomposite rubber of polybutyl acrylate and poly2-ethylhexyl(meth)acrylate, butyl acrylate-butadiene copolymer rubber, butylacrylate-styrene copolymer rubber, and the like. The acrylic rubbers maybe used alone or in admixture thereof. The term “copolymer” as usedherein comprehends random copolymers, block copolymers, graft copolymersand combinations thereof.

The acrylic rubber latex can be obtained by polymerizing a monomermixture of an alkyl (meth)acrylate monomer, a polyfunctional monomercontaining at least two polymerizable unsaturated bonds in its molecule,other copolymerizable monomers and the like in the presence of a radicalpolymerization initiator and optionally a chain transfer agent accordingto a conventional emulsion polymerization method, for example, bymethods as described in JP-A-50-88169 and JP-A-61-141746.

The alkyl (meth)acrylate monomer is a component which constitutes themain backbone of the acrylic rubber. Examples thereof are, for instance,an alkyl acrylate having a C₁ to C₁₂ alkyl group such as methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate or2-ethylhexyl acrylate, an alkyl methacrylate having a C₄ to C₁₂ alkylgroup such as 2-ethylhexyl methacrylate or lauryl methacrylate, and thelike. These may be used alone or in admixture thereof. Of these, amonomer mixture containing 40 to 100% by weight, especially 60 to 100%by weight, of butyl acrylate is preferred from the viewpoints of lowglass transition temperature of the obtained polymers and economy, inwhich the residual comonomer is for instance methyl acrylate, ethylacrylate, 2-ethylhexyl acrylate or the like.

The polyfunctional monomer containing at least two polymerizableunsaturated bonds in its molecule is a component used for introducing acrosslinked structure to the acrylic rubber particles to form a networkstructure, thereby exhibiting a rubber elasticity, and for providing anactive site for grafting of vinyl monomers mentioned after. Examples ofthe polyfunctional monomer are, for instance, dially phthalate, triallylcyanurate, trially isocyanurate, allyl methacrylate, ethyleneglycoldimethacrylate, divinyl benzene, other known allyl, di(meth)acrylate anddivinyl compounds, and the like. These may be used alone or in admixturethereof. Of these, allyl methacrylate, triallyl cyanurate, triallyisocyanurate and diallyl phthalatae are preferred from the viewpoints ofcrosslinking efficiency and grafting efficiency.

The other copolymerizable monomer may be optionally used for the purposeof adjusting the refractive index of the obtained acrylic rubbers or theaffinity with silicone rubbers. Examples thereof are, for instance,methacrylic acid, a methacrylic ester monomer such as methylmethacrylate, ethyl methacrylate, glycidyl methacrylate, hydroxyethylmethacrylate or benzyl methacrylate, an aromatic vinyl monomer such asstyrene or α-methylstyrene, a vinyl cyanide monomer such asacrylonitrile or methacrylonitrile, a silicon-containing vinyl monomersuch as γ-methacryloyloxypropyldimethoxymethylsilane,γ-methacryloyloxypropyltrimethoxysilane or trimethylvinylsilane, and thelike. These may be used alone or in admixture thereof.

Preferable proportions of the monomers used in the production of acrylicrubber latex are from 66.5 to 99.9% by weight, especially 85 to 99.9% byweight, of the alkyl (meth)acrylate monomer, 0.1 to 10% by weight,especially 0.1 to 5% by weight of the polyfunctional monomer containingtwo or more polymerizable unsaturated bonds in its molecule, and 0 to23.4% by weight, especially 0 to 14.9% by weight, of the othercopolymerizable monomer, the total thereof being 100% by weight. If theproportion of the alkyl (meth)acrylate monomer is too small, theproducts lack properties as a rubber, so the impact resistance-impartingeffect is lowered. If the proportion of the alkyl (meth)acrylate is toolarge, the proportion of the polyfunctional monomer becomes too small,so the effects to be produced thereby tend to be insufficient. Also, ifthe proportion of the polyfunctional monomer is too small, thecrosslinking density is low, so the impact resistance-imparting effecttends to be lowered, and if the proportion is too large, thecrosslinking density becomes too high, so the impactresistance-imparting effect also tends to be lowered. The othercopolymerizable monomer is a component used for adjusting the refractiveindex or the impact resistance and, when it is desired to obtain theeffects to be produced by the use thereof, the amount thereof ispreferably not less than 0.1% by weight.

As the radical polymerization initiator used in the emulsionpolymerization for the preparation of the acrylic rubber latex and thechain transfer agent optionally used therein, those used in usualradical polymerization can be used without particular restriction.

Examples of the radical polymerization initiator are an organic peroxidesuch as cumene hydroperoxide, tert-butyl hydroperoxide, benzoylperoxide, tert-butylperoxy isopropylcarbonate, di-tert-butyl peroxide,tert-butylperoxy laurate, lauroyl peroxide, succinic acid peroxide,cyclohexanone peroxide or acetylacetone peroxide; an inorganic peroxidesuch as potassium persulfate or ammonium persulfate; an azo compoundsuch as 2,2′-azobisisobutylonitrile or2,2′-azobis-2,4-dimethylvaleronitrile; and the like. Of these, organicperoxides and inorganic peroxides are preferably used from the viewpointof a high reactivity.

In case of using organic peroxides or inorganic peroxides, they may beused in combination with a reducing agent, e.g., a mixture of ferroussulfate/glucose/sodium pyrophosphate, a mixture of ferroussulfate/dextrose/sodium pyrophosphate, or a mixture of ferroussulfate/sodium formaldehyde sulfoxylate/ethylenediamineacetate. The useof a reducing agent is particularly preferable, since the polymerizationtemperature can be lowered.

The radical polymerization initiator is used usually in an amount of0.005 to 10 parts by weight, preferably 0.01 to 5 parts by weight, morepreferably 0.02 to 2 parts by weight, per 100 parts by weight of amonomer mixture used. If the amount of the initiator is too small, therate of polymerization is low, so the production efficiency tends to belowered, and if the amount is too large, the molecular weight of theobtained polymers is lowered, so the impact resistance tends to belowered.

Examples of the chain transfer agent are, for instance,t-dodecylmercaptan, n-octylmercaptane, n-tetradecylmercaptan,n-hexylmercaptan and the like.

The chain transfer agent is an optional component. From the viewpoint ofexhibiting the impact resistance-imparting effect, it is preferable thatthe amount thereof is from 0.001 to 5 parts by weight per 100 parts byweight of the monomer mixture.

Examples of the emulsifier used in emulsion polymerization for theproduction of acrylic rubbers are, besides emulsifiers which can be usedin the production of silicone rubber latex (A), fatty acid metal saltssuch as potassium oleate, sodium oleate, potassium rhodinate, sodiumrhodinate, potassium palmitate, sodium palmitate and potassium stearate.These may be used alone or in admixture thereof.

The silicone rubber latex (A) and the acrylic rubber latex (B) are usedpreferably in such a ratio that the amount of silicone(polyorganosiloxane) is from 1 to 90% by weight, especially from 1 to50% by weight, more especially from 1 to 20% by weight, based on thewhole rubber component (silicone rubber plus acrylic rubber). An effectof imparting a high impact resistance to thermoplastic resins isobtained within this range. If the amount of the silicone included inthe whole rubber component is too small or too large, improvement inimpact resistance of thermoplastic resins tends to become insufficient.

In case that the amount of silicone is more than 50% by weight, it ispreferable from the viewpoint of exhibiting impact resistance that theactive sites for grafting are present in the silicone rubber, in otherwords, graft copolymers are produced by polymerization of vinyl monomersmentioned after. It is also preferable from the viewpoint of impactresistance that the acrylic rubber has active sites for graftingregardless of the amount of silicone.

From the viewpoint of easiness in particle size enhancement bycoagglomeration, it is preferable that the solid concentration of thewhole rubber latex (mixture of silicone rubber latex and acrylic rubberlatex) is from 10 to 50% by weight, especially from 20 to 40% by weight.

The rubber-modified resin of the present invention is obtained bypolymerizing a vinyl monomer in the presence of the mixed rubber latexand, during the polymerization, coagglomerating the polymer particles inthe latex to enhance the particle size.

The rubber-modified resin comprises, as mentioned above, resin particlescontaining particles formed by particle size-enhancing co-agglomerationof graft copolymer particles wherein a vinyl monomer isgraft-polymerized onto silicone rubber particles of silicone rubberlatex (A) (or particles wherein the silicone rubber and a vinyl polymerare physically coexist if the silicone rubber particles have no graftingsite) and graft copolymer particles wherein the vinyl monomer isgraft-polymerized onto acrylic rubber particles (or particles whereinthe acrylic rubber and the vinyl polymer are physically coexist if theacrylic rubber particles have no grafting site). It is preferable thatthe average particle size of the resin particles is not less than 100nm, especially not less than 120 nm, and is not more than 1,000 nm,especially not more than 800 nm. If the average particle size is lessthan 100 nm or more than 1,000 nm, the impact resistance tends to lower.It is preferable that the content of a solvent-insoluble matter in therubber-modified resin is not less than 40% by weight, especially notless than 70% by weight, more especially not less than 80% by weight.

The “coagglomeration to enhance particle size” or “particle sizeenhancement by coagglomeration” denotes simultaneously agglomerating atleast two kinds of polymer particles having different chemicalcompositions in the same system to enhance the particle size.

The particle size-enhancing coagglomeration can be carried out by aconventional method using an electrolyte, for example, by adding, priorto the step of polymerizing a vinyl monomer or during this step, aninorganic salt such as sodium sulfate, an inorganic acid such ashydrochloric acid, an organic acid such as acetic acid, or a latex of anon-crosslinked acid group-containing copolymer obtained bycopolymerization of an unsaturated acid monomer and an alkyl(meth)acrylate monomer as disclosed in JP-A-50-25655, JP-A-8-12703 andJP-A-8-12704, to the polymerization system. When it is desired to obtaina rubber-modified resin having an average particle size of 100 to 400nm, it is preferable to use an inorganic salt, an inorganic acid or anorganic acid. An inorganic salt is particularly preferred since anoperation for adjusting the pH of the system after the completion of thecoagglomeration is omitted. When it is desired to obtain arubber-modified resin having an average particle size of 300 to 1,000nm, it is preferable to use the acid group-containing copolymer latex.

An example of the acid group-containing copolymer is, for instance,copolymers of 5 to 25% by weight, especially 5 to 15% by weight, of atleast one unsaturated acid such as acrylic acid, methacrylic acid,itaconic acid or crotonic acid, 45 to 95% by weight, especially 65 to95% by weight, of at least one alkyl (meth)acrylate having a C₁ to C₁₂alkyl group (preferably a mixture of 10 to 80% by weight of an alkylacrylate having a C₁ to C₁₂ alkyl group and 20 to 90% by weight of analkyl methacrylate having a C₁ to C₁₂ alkyl group), and 0 to 30% byweight, especially 0 to 20% by weight, of at least one other vinylmonomer copolymerizable therewith.

In case of using an inorganic salt, an inorganic acid or an organic acidas an electrolyte, preferably the amount thereof is from 0.1 to 5 partsby weight, especially 0.2 to 4 parts by weight, more especially 0.3 to 3parts by weight, per 100 parts by weight (solid basis) of the mixedrubber latex. If the amount is too small, the coagglomeration tends tobe difficult. If the amount is too large, there is a tendency that it isdifficult to apply to industrial production since clots are easy to beproduced.

In case of using an acid group-containing copolymer latex as anelectrolyte, preferably the amount thereof is from 0.1 to 10 parts byweight, especially 0.2 to 5 parts by weight, per 100 parts by weight(solid basis) of the mixed rubber latex. If the amount is too small, thecoagglomeration tends to occur with difficulty. If the amount is toolarge, unfavorable phenomenon such as lowering of impact resistance iseasy to occur.

The time of adding an electrolyte such as inorganic salt, inorganicacid, organic acid or acid group-containing copolymer latex to thepolymerization system to enhance the particle size is not particularlylimited so long as the coagglomeration takes place during the step ofpolymerizing a vinyl monomer in the presence of rubber particles. Fromthe viewpoint of impact resistance, it is preferable to add theelectrolyte to the polymerization system prior to starting thepolymerization or until 90% by weight of a vinyl monomer used for thepolymerization is polymerized (polymerization conversion 0 to 90% byweight), especially during the period after not less than 10% by weightof the vinyl monomer used for the polymerization is polymerized anduntil 70% by weight of the vinyl monomer used for the polymerization ispolymerized (polymerization conversion 10 to 70% by weight), moreespecially during the period after not less than 10% by weight of thevinyl monomer used for the polymerization is polymerized and until 50%by weight of the vinyl monomer used for the polymerization ispolymerized (polymerization conversion 10 to 50% by weight). Afteradding the electrolyte, the polymerization is further continued tocomplete the polymerization. Preferably, the polymerization is carriedout until the polymerization conversion of the vinyl monomer reaches atleast 95% by weight.

The polymerization temperature is from 30 to 90° C., preferably from 40to 80° C.

The vinyl monomer polymerized in the mixed rubber latex is a componentfor raising the affinity of a rubber-modified resin with a thermoplasticresin to thereby uniformly disperse the rubber-modified resin into thethermoplastic resin in the case that the thermoplastic resin isincorporated with the rubber-modified resin and molded.

Examples of the vinyl monomer are, for instance, an aromatic vinylmonomer such as styrene, α-methylstyrene, p-methylstyrene or divinylbenzene, a vinyl cyanide monomer such as acrylonitrile ormethacrylonitrile, a halogenated vinyl monomer such as vinyl chloride,vinylidene chloride or vinylidene fluoride, methacrylic acid, amethacrylic ester monomer such as methyl methacrylate, ethylmethacrylate, butyl methacrylate, glycidyl methacrylate, hydroxyethylmethacrylate, ethylene glycol dimethacrylate or 1,3-butylene glycoldimethacrylate, acrylic acid, an acrylic ester monomer such as methylacrylate, butyl acrylate, glycidyl acrylate or hydroxybutyl acrylate,and the like. The vinyl monomers may be used alone or in admixturethereof. Also, one or at least two vinyl monomers may be added andpolymerized in multistages. Of these, from the viewpoints of easiness inparticle size enhancement by coagglomeration and impact resistance ispreferred a monomer mixture containing 50 to 100% by weight, especially70 to 100% by weight, of a methacrylic ester monomer and/or an acrylicester monomer, the rest of which may be the above-mentioned aromaticvinyl monomer, vinyl cyanide monomer, halogenated vinyl monomer and thelike.

Preferably, the vinyl monomer is used in an amount of 2 to 60 parts byweight, especially 5 to 40 parts by weight, more especially 8 to 20parts by weight, while the amount of the whole rubber latex (solidbasis) is from 40 to 98 parts by weight, especially 60 to 95 parts byweight, more especially 80 to 92 parts by weight, wherein the totalthereof is 100 parts by weight. If the amount of the vinyl monomer istoo large, there is a tendency that impact resistance is notsufficiently exhibited, since the content of rubber component becomestoo small. If the amount of the vinyl monomer is too small, the handlingtends to become difficult since the powdery state of the rubber-modifiedresin is deteriorated.

The polymerization of the vinyl monomer can be carried out by aconventional emulsion polymerization. As a radical polymerizationinitiator used therein and a chain transfer agent and an emulsifierwhich are optionally used therein, there may be used those usable in theproduction of the acrylic rubber latex. The limitations concerning theamounts of them in the production of the acrylic rubber latex are alsoapplicable to this case.

The rubber-modified resin obtained by the polymerization of the vinylmonomer may be isolated as a powder from the obtained latex or may beused in the form of the latex. The isolation of the polymer may becarried out in a usual manner, for example, by adding a metal salt suchas calcium chloride, magnesium chloride or magnesium sulfate, or aninorganic or organic acid such as hydrochloric acid, sulfuric acid,phosphoric acid or acetic acid, to the latex to coagulate the latex,separating, washing with water, dehydrating and drying the polymer. Aspray-drying method is also applicable.

The thus obtained rubber-modified resin (in the state of powder orlatex) is incorporated into various thermoplastic resins to givethermoplastic resin compositions having an improved impact resistance.

Examples of the thermoplastic resin are, for instance, polyvinylchloride, chlorinated polyvinyl chloride, polystyrene,styrene-acrylonitrile copolymer, styrene-acrylonitrile-N-phenylmaleimidecopolymer, α-methylstyrene-acrylonitrile copolymer, polymethylmethacrylate, methyl methacrylate-styrene copolymer, polycarbonate,polyamide, a polyester such as polyethylene terephthalate, polybutyleneterephthalate or 1,4-cyclohexanedimethanol-modified polyethyleneterephthalate, butadiene rubber-styrene copolymer (HIPS resin),acrylonitrile-butadiene rubber-styrene copolymer (ABS resin),acrylonitrile-acrylic rubber-styrene copolymer (AAS resin),acrylonitrile-ethylenepropylene rubber-styrene copolymer (AES resin),polyphenylene ether, and the like. These may be used alone or inadmixture thereof. Examples of a combination of at least two resins area mixed resin of 5 to 95% by weight of polycarbonate and 5 to 95% byweight of HIPS resin, ABS resin, AAS resin or AES resin (total thereof100% by weight), and a mixed resin of 5 to 95% by weight ofpolycarbonate and 5 to 95% by weight of polyethylene terephthalate orpolybutylene terephthalate (total thereof 100% by weight).

It is preferable, from the viewpoint of a balance of physicalproperties, that the amount of the rubber-modified resin is from 0.1 to150 parts by weight, especially from 0.5 to 120 parts by weight, per 100parts by weight of a thermoplastic resin. If the amount is too small,the impact resistance of thermoplastic resins is not sufficientlyimproved, and if the amount is too large, it is difficult to maintainthe properties such as rigidity and surface hardness of thethermoplastic resins.

Mixing of a thermoplastic resin with a solid powder of therubber-modified resin can be carried out by firstly mixing them througha Henschel mixer, a ribbon mixer or the like and then melt-kneading themixture through a roll mill, an extruder, a kneader or the like.

The thermoplastic resin compositions of the present invention maycontain usual additives, e.g., plasticizer, stabilizer, lubricant,ultraviolet absorber, antioxidant, flame retardant, pigment, glassfiber, filler, polymer processing aid, polymer lubricant andantidropping agent. For example, preferable examples of the flameretardant are a phosphorus compound such as triphenyl phosphate,condensed phosphate or stabilized red phosphorus, a silicone compoundsuch as phenyl group-containing polyorganosiloxane copolymer, and thelike. Preferable examples of the polymer processing aid are methacrylate(co)polymers such as methyl methacrylate-butyl acrylate copolymer.Preferable examples of the antidropping agent are fluorocarbon resinssuch as polytetrafluoroethylene. Preferable amounts of these additivesare, from the viewpoint of effect-cost balance, 0.1 to 30 parts byweight, especially 0.2 to 20 parts by weight, more especially 0.5 to 10parts by weight, per 100 parts by weight of a thermoplastic resin.

The thermoplastic resin composition can also be obtained by mixing alatex of a thermoplastic resin with a latex of the rubber-modified resinand subjecting the mixed latex to coprecipitation of polymer particles.

Molding methods conventionally used for thermoplastic resincompositions, e.g., injection molding, extrusion, blow molding andcalendering, are applicable to the thermoplastic resin compositions ofthe present invention.

The obtained molded articles have excellent impact resistance ascompared with those using conventional impact modifiers.

The present invention is more specifically explained by means ofexamples, but it is to be understood that the present invention is notlimited to only these examples. In the following examples andcomparative examples, all parts and % excepting variation coefficientare by weight unless otherwise noted.

In the following examples and comparative examples, evaluation was madein the following manners.

[Solid Concentration of Latex and Polymerization Conversion]

A sample of a latex obtained after reaction was dried in a hot air dryerat 120° C. for 1 hour to measure the solid concentration (heatingresidue). The polymerization conversion of a rubber latex was calculatedaccording to the equation: (amount of solid matter/amount of monomerscharged)×100 (%).

[Average Particle Size]

Using as a measuring apparatus MICROTRAC UPA made by LEED & NORTHRUPINSTRUMENTS, the volume average particle size (nm) and the variationcoefficient in particle size distribution (standard deviation/volumeaverage particle size)×100 (%) were measured by a light scatteringmethod.

[Content of Solvent-insoluble Matter (Gel Fraction)]

A latex was dried firstly at 50° C. for 75 hours and then at roomtemperature for 8 hours under reduced pressure to give a test sample.The sample was immersed in toluene for 24 hours and centrifuged at12,000 r.p.m. for 60 minutes, and the weight percentage of thetoluene-insoluble matter in the sample was calculated.

[Izod Impact Strength]

The Izod impact strength was measured at −30° C., 0° C. and 23° C. byusing a notched ¼ inch bar or a notched ⅛ inch bar according to ASTMD-256.

[Flame Resistance]

Evaluation was made by UL94 V test.

PREPARATION EXAMPLE 1

Preparation of Silicone Rubber Latex (A-1)

A five-necked flask equipped with a stirrer, a reflux condenser, aninlet for introducing nitrogen gas, an inlet for introducing monomersand a thermometer was charged with the following ingredients.

Ingredients Amount (part) Pure water 189 Sodium dodecylbenzenesulfonate(SDBS) 0.5

The temperature was then raised to 70° C. with purging the system withnitrogen gas. Subsequently, after adding 1 part of pure water and 0.02part of potassium persulfate to the system, a mixed liquid of thefollowing ingredients was added at a time to the system, and was stirredfor 1 hour to complete the polymerization, thus giving a latex of ST-BMAcopolymer.

Ingredients Amount (part) Styrene (ST) 0.7 Butyl methacrylate (BMA) 1.3

The polymerization conversion was 99%. The obtained latex had a solidcontent of 1.0%, an average particle size of 10 nm and a variationcoefficient of 38%. Also, the content of solvent-insoluble matter in theST-BMA copolymer was 0%.

Separately, an emulsion of a silicone rubber-forming component wasprepared by stirring a mixture of the following ingredients at 10,000r.p.m. for 5 minutes with a homogenizer.

Ingredients Amount (part) Pure water 70 SDBS 0.5Octamethylcyclotetrasiloxane 94 Vinyltriethoxysilane (VTES) 2Tetraethoxysilane (TEOS) 2

Subsequently, the latex containing ST-BMA copolymer was kept at 80° C.,and thereto were added 2 parts of dodecylbenzene sulfonic acid and 18parts of pure water to adjust the system to pH 1.7. The above emulsionof silicone rubber-forming component was added at a time to the latex.The resulting mixture was stirred for 6 hours, and after cooling to 25°C. and allowing to stand for 20 hours, the mixture was adjusted to pH8.4 with sodium hydroxide to finish the polymerization, thus giving asilicone rubber latex (A-1). The polymerization conversion of thesilicone rubber-forming component was 85%. The obtained latex (A-1) hada solid concentration of 23%, an average particle size of 90 nm and avariation coefficient in particle size distribution of 39%. Also, thecontent of solvent-insoluble matter was 71%. The silicone rubber in thesilicone rubber latex was composed of 98% of silicone component and 2%of ST-BMA copolymer component, which were calculated based on the chargeand conversion.

Preparation Example 2

Preparation of Silicone Rubber Latex (A-2)

Silicone rubber latex (A-2) was prepared in the same manner as inPreparation Example 1 except that vinyltriethoxysilane (VTES) wasreplaced with tetraethoxysilane (TEOS) so that the total amount of TEOSwas 3 parts. The obtained latex (A-2) had a solid concentration of 23%,an average particle size of 85 nm and a variation coefficient inparticle size distribution of 37%. Also, the content of solventinsoluble matter was 81%. The silicone rubber in the silicone rubberlatex was composed of 98% of silicone component and 2% of ST-BMAcopolymer component, which were calculated based on the charge andconversion.

Preparation Example 3

Preparation of Acrylic Rubber Latex (B-1)

A five-necked flask equipped with a stirrer, a reflux condenser, aninlet for introducing nitrogen gas, an inlet for introducing monomersand a thermometer was charged with the following ingredients at a time.

Ingredients Amount (part) Pure water 200 Sodium oleate 1.3

The temperature was then raised to 70° C. with stirring in a nitrogenstream. After reaching 70° C., a mixture of the following ingredientswas added at a time to the system, and 0.05 part of potassium persulfatewas further added. The resulting mixture was stirred at 70° C. for 1hour.

Ingredients Amount (part) Butyl acrylate (BA) 4 Allyl methacrylate(AlMA) 0.04

Subsequently the following mixture was added dropwise over 5 hours, andafter the completion of the addition, the mixture was further stirredfor 1 hour to complete the polymerization.

Ingredients Amount (part) BA 96 AlMA 0.96

The polymerization conversion was 99%. The obtained latex had a solidconcentration of 33%, an average particle size of 80 nm and a variationcoefficient of 28%. Also, the content of solvent-insoluble matter was96%.

EXAMPLE 1

A five-necked flask equipped with a stirrer, a reflux condenser, aninlet for introducing nitrogen gas, an inlet for introducing monomersand a thermometer was charged with the following ingredients at a time.

Ingredients Amount (part) Pure water 240 Silicone rubber latex (A-1)(solid basis) 11.9 Acrylic rubber latex (B-1) (solid basis) 73.1

The temperature was then raised to 70° C. with stirring in a nitrogenstream and, after reaching 70° C., 0.03 part of potassium persulfate wasadded. Subsequently, 15 parts of methyl methacrylate (MMA) was addeddropwise over 1 hour, during which 1.2 parts of sodium sulfate was addedto enhance the particle size by agglomeration when 3 parts of MMA hadbeen added. After the completion of the addition, stirring was furthercontinued to complete the polymerization, thus giving a latex ofrubber-modified resin (I). The polymerization conversion was 99%. Theobtained rubber-modified resin particles had an average particle size of185 nm and a solvent-insoluble matter content of 90%.

The obtained latex was diluted with pure water to 15% in solidconcentration, and thereto was added 2 parts of calcium chloride tocoagulate the latex. The resulting slurry was once heated to 80° C., andwas then cooled, dehydrated and dried to give a powder ofrubber-modified resin (I).

Into 100 parts of a vinyl chloride resin having a degree ofpolymerization of 800 were incorporated 7.0 parts of the rubber-modifiedresin (I), 3.0 parts of octyl tin mercaptide, 1.0 part of stearylalcohol, 0.5 part of stearic acid amide, 0.5 part of montanic acid diolester, 0.5 part of titanium oxide and 1.0 part of a high molecularprocessing aid commercially available under the trade mark of KANE ACEPA20 made by Kaneka Corporation. The mixture was melt-kneaded by a 50 mmsingle screw extruder (model VS50-26 made by Tanabe Plastic KikaiKabushiki Kaisha) to give pellets. The obtained pellets were molded byan injection molding machine (model IS-170G made by Toshiba Machine Co.,Ltd.) at a cylinder temperature of 195° C. to give ¼ inch Izod impacttest specimens. The results of the Izod impact test are shown in Table1.

EXAMPLE 2

A powder of rubber-modified resin (II) was prepared in the same manneras in Example 1 except that the silicone rubber latex (A-2) was usedinstead of the silicone rubber latex (A-1). The polymerizationconversion was 99%. The obtained rubber-modified resin particles had anaverage particle size of 180 nm and a solvent-insoluble matter contentof 89%.

The Izod impact test was made in the same manner as in Example 1 exceptthat the rubber-modified resin (II) was used instead of therubber-modified resin (I). The results are shown in Table 1.

EXAMPLE 3

A powder of rubber-modified resin (III) was prepared in the same manneras in Example 1 except that a monomer mixture of 75% of ST and 25% ofacrylonitrile was used instead of MMA. The polymerization conversion was96%. The obtained rubber-modified resin particles had an averageparticle size of 160 nm and a solvent-insoluble matter content of 88%.

The Izod impact test was made in the same manner as in Example 1 exceptthat the rubber-modified resin (III) was used instead of therubber-modified resin (I). The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

Polymerization of a vinyl monomer in the presence of rubber particleswas carried out without coagglomerating the rubber particles to enhancethe particle size.

That is to say, a powder of rubber-modified resin (I′) was prepared inthe same manner as in Example 1 except that sodium sulfate was notadded. The polymerization conversion was 99%. The obtainedrubber-modified resin particles had an average particle size of 85 nmand a solvent-insoluble matter content of 89%.

The Izod impact test was made in the same manner as in Example 1 exceptthat the rubber-modified resin (I′) was used instead of therubber-modified resin (I). The results are shown in Table 1.

COMPARATIVE EXAMPLE 2

Polymerization of a vinyl monomer in the presence of rubber particleswas carried out in the same manner as in Example 1 except that acomposite rubber previously obtained by particle size enhancingcoagglomeration was used instead of adding an electrolyte during thepolymerization.

That is to say, a flask was charged with 240 parts of pure water, 11.9parts (solid basis) of silicone rubber latex (A-1) and 73.1 parts (solidbasis) of acrylic rubber latex (B-1) to give a mixed rubber latex. Tothe mixed rubber latex were added 0.7 part of acetic acid and then 0.5part of NaOH at 70° C. in a nitrogen stream to give a coagglomeratedrubber of enhanced particle size (composite rubber). The averageparticle size of the composite rubber was 175 nm.

To the obtained composite rubber latex was added dropwise 15 parts ofMMA over 1 hour. After the completion of the addition, the reactionmixture was further stirred for 1 hour to complete the polymerization,thus giving graft copolymer (II′) particles. The polymerizationconversion was 99%. The obtained graft copolymer particles had anaverage particle size of 185 nm and a solvent-insoluble matter contentof 90%.

The Izod impact test was made in the same manner as in Example 1 exceptthat the graft copolymer (II′) was used instead of the rubber-modifiedresin (I). The results are shown in Table 1.

TABLE 1 Com. Com. Ex.1 Ex.2 Ex.3 Ex.1 Ex.2 Izod impact 23° C. 65 55 3513 20 strength (kJ/m²) 0° C. 11 10 9 7 8

From the results shown in Table 1, it would be understood that a higheffect of improving impact resistance is exhibited by the use of therubber-modified resin of the present invention as an impact modifier forvinyl chloride resins.

EXAMPLE 4

Into 100 parts of a polycarbonate resin comprising2,2-bis(4-hydroxyphenyl)propane as a bisphenol component and having aweight average molecular weight of 23,000 were incorporated 3 parts ofthe rubber-modified resin (I) obtained in Example 1, 0.3 part of aphenolic stabilizer (TOPANOL CA made by ZENECA) and 0.3 part of aphosphorus stabilizer (ADEKASTAB PEP36 made by Asahi Denka Kogyo K. K).The mixture was melt-kneaded by a 40 mm single screw extruder (modelHW-40-28 made by Tabata Kikai Kabushiki Kaisha) to give pellets. Theobtained pellets were dried at 110° C. for more than 5 hours and moldedby an injection molding machine (model FAS100B made by Kabushiki KaishaFANUC) at a cylinder temperature of 290° C. to give ¼ inch Izod impacttest specimens. The specimens were subjected to the Izod impact test.The results are shown in Table 2.

COMPARATIVE EXAMPLE 3

The Izod impact test was made in the same manner as in Example 4 exceptthat the graft copolymer (II′) obtained in Comparative Example 2 wasused instead of the rubber-modified resin (I). The results are shown inTable 2.

TABLE 2 Example 4 Com. Ex. 3 Izod impact strength 68 59 (kJ/m2) at 23°C.

From the results shown in Table 2, it would be understood that in caseof using the rubber-modified resin of the present invention as an impactmodifier for polycarbonate resins, it exhibits a higher effect ofimproving impact resistance as compared with a graft copolymercontaining a composite rubber composed of a silicone rubber and anacrylic rubber.

EXAMPLES 5 AND 6

A latex of rubber-modified resin (IV) was prepared in the same manner asin Example 1 except that in the preparation of rubber-modified resin (I)of Example 1, there were changed the amount of silicone rubber latex(A-1) to 18 parts (solid basis), the amount of acrylic rubber latex(B-1) to 72 parts (solid basis), the amount of MMA to 10 parts and theamount of sodium sulfate to 1.5 parts. The polymerization conversion ofMMA was 99%. The obtained rubber-modified resin particles had an averageparticle size of 190 nm and a solvent-insoluble matter content of 86%.The obtained latex was subjected to a coagulation treatment in the samemanner as in Example 1 to give a powder of rubber-modified resin (IV).

A composition was prepared using the obtained rubber-modified resin (IV)according to the recipe shown in Table 3, and was melt-kneaded by a twinscrew extruder (model TEX44S made by The Japan Steel Works, Ltd.) togive pellets. The obtained pellets were dried at 110° C. for more than 5hours and molded by an injection molding machine (model FAS100B made byKabushiki Kaisha FANUC) at a cylinder temperature of 280° C. to give ⅛inch test specimens for Izod impact test and {fraction (1/16)} inch testspecimens for flame resistance evaluation. Using these specimens, theIzod impact test and flame resistance evaluation were made. The resultsare shown in Table 3.

COMPARATIVE EXAMPLES 4 and 5

In Comparative Example 4, the procedure of Example 5 was repeated exceptthat the rubber-modified resin (I) was replaced with a silicone flameretardant (KR-219 made by Shin-Etsu Chemical Co., Ltd.) and the flameretardant KR-219 was used in an amount of 8 parts.

In Comparative Example 5, the procedure of Example 5 was repeated exceptthat the rubber-modified resin (I) was not used without the replacementthereof with the silicone flame retardant.

The results of the Izod impact test and flame resistance evaluation areshown in Table 3.

COMPARATIVE EXAMPLES 6 and 7

In Comparative Example 6, the procedure of Example 6 was repeated exceptthat the rubber-modified resin (I) was not used.

In Comparative Example 7, the procedure of Example 6 was repeated exceptthat the rubber-modified resin (I) and the phosphorus-based flameretardant triphenyl phosphate were not used.

The results of the Izod impact test and flame resistance evaluation areshown in Table 3.

TABLE 3 Com. Com. Com. Com. Ex.5 Ex.6 Ex.4 Ex.5 Ex.6 Ex.7 Thermoplasticresin PC 90 70 90 90 70 70 PET 10 30 10 10 30 30 Impact modifier 2 3.5 00 0 0 Rubber-modified resin (IV) Flame retardant KR-219 6 0 8 0 0 0Triphenyl 0 5 0 0 5 0 phosphate Antidropping 0.5 0.3 0.5 0.5 0.3 0.3agent PTFE Stabilizer AO-60 0.1 0.2 0.1 0.1 0.2 0.2 PEP-36 0.1 0.3 0.10.1 0.3 0.3 Izod impact strength 80 35 8 35 9 10 at 23° C. (kJ/m²) UL94V V-1 V-0 V-1 below V-0 below standard standard The ingredients shown inTable 3 are as follows: PC: Polycarbonate resin comprising2,2-bis(4-hydroxyphenyl)propane as a bisphenol component and having aweight average molecular weight of 23,000 PET: Polyethyleneterephthalate resin having a logarithmic viscosity of 0.75 KR-219:Silicone flame retardant KR-219 made by Shin-Etsu Chemical Co., Ltd.PTFE: Polytetrafluoroethylene AO-60: Phenolic stabilizer (ADEKASTABPEP36 made by Asahi Denka Kogyo K.K) PEP36: Phosphorus stabilizer(ADEKASTAB PEP36 made by Asahi Denka Kogyo K.K)

From the results shown in Table 3, it is found that the rubber-modifiedresin of the present invention can improve the impact resistance of apolycarbonate/polyethylne terephthalate blend flame-retarded by asilicone flame retardant or a phosphorus flame retardant whilemaintaining the flame resistance of the blend.

EXAMPLE 7

Into 70 parts of a polycarbonate resin (LEXANE 121 made by GE PlasticsJapan Ltd.) and 30 parts of an ABS resin (SUNTAC AT05 made by MitsuiChemicals, Inc.) were incorporated 5 parts of the rubber-modified resin(I) obtained in Example 1, 0.3 part of a phenolic stabilizer (TOPANOL CAmade by ZENECA) and 0.3 part of a phosphorus stabilizer (ADEKASTAB PEP36made by Asahi Denka Kogyo K. K). The mixture was melt-kneaded by a 40 mmsingle screw extruder (model HW-40-28 made by Tabata Kikai KabushikiKaisha) to give pellets. The obtained pellets were dried at 110° C. formore than 5 hours and molded by an injection molding machine (modelFAS100B made by Kabushiki Kaisha FANUC) at a cylinder temperature of260° C. to give ¼ inch Izod impact test specimens. The specimens weresubjected to the Izod impact test. The results are shown in Table 4.

COMPARATIVE EXAMPLE 8

The procedure of Example 7 was repeated except that the rubber-modifiedresin (I) was not used. The results of Izod impact test are shown inTable 4.

TABLE 4 Example 7 Com. Ex. 8 Izod impact 23° C. 49 45 strength (kJ/m²)−30° C. 16 10

From the results shown in Table 4, it is found that the rubber-modifiedresin of the present invention also exhibits an effect of improvingimpact resistance on a polycarbonate/ABS resin blend.

INDUSTRIAL APPLICABILITY

According to the present invention, rubber-modified resins having aremarkably improved impact resistance-imparting effect can be obtainedby conducting polymerization of vinyl monomers in the presence of asilicone rubber latex and an acrylic rubber latex, during which polymerparticles are coagglomerated to enhance the particle size. Therubber-modified resins are applicable to various thermoplastic resins asimpact modifier, and thermoplastic resin compositions comprising therubber-modified resin and a thermoplastic resin have excellent impactresistance.

What is claimed is:
 1. A rubber-modified resin product, comprising: a)silicone rubber particles, each silicone rubber particle having a vinylmonomer graft polymerized thereon; b) acrylic rubber particles, eachacrylic rubber particle having a vinyl monomer graft polymerizedthereon; said graft polymerized silicone rubber particles and said graftpolymerized acrylic rubber particles being coagglomerated and having avinyl monomer polymerized onto said coagglomeration in a polymerizationsystem wherein polymerization conversion of the vinyl monomer which ispolymerized onto said coagglomeration is carried out by adding anelectrolyte to the polymerization system when the conversion has reached10% to 70% by weight.
 2. The rubber-modified resin of claim 1, whereinthe amount of silicone is from 1 to 90% by weight based on 100% byweight of the whole rubber component.
 3. The rubber-modified resin ofclaim 1 or 2, wherein 2 to 60 parts by weight of the vinyl monomer ispolymerized in the presence of 40 to 98 parts by weight (solid basis) ofthe whole rubber latex, the total thereof being 100 parts by weight. 4.The rubber-modified resin of claim 1 or 2, wherein said vinyl monomer isat least one member selected from the group consisting of aromatic vinylmonomers, vinyl cyanide monomers, halogenated vinyl monomers,(meth)acrylic acid and (meth)acrylic esters.
 5. A thermoplastic resincomposition comprising 100 parts by weight of a thermoplastic resin and0.1 to 150 parts by weight of the rubber-modified resin of claim
 1. 6.The composition of claim 5, wherein the vinyl monomer used in thepreparation of said rubber-modified resin is at least one memberselected from the group consisting of aromatic vinyl monomers, vinylcyanide monomers, halogenated vinyl monomers, (meth)acrylic acid end(meth)acrylic esters.
 7. The composition of claim 5 or 6, wherein saidthermoplastic resin is at least one member selected from the groupconsisting of polyvinyl chloride, chlorinated polyvinyl chloride,polystyrene, styrene-acrylonitrile copolymer,styrene-acrylonitrile-N-phenylmateimide copolymer,α-methylstyrene-acrylonitrile copolymer, polymethyl, methacrylate,methyl methacrylate-styrene copolymer, polycarbonate, polyamide,polyester, HIPS resin, ABS resin, AAS resin, AES resin and polyphenyleneether.
 8. The rubber-modified resin of claim 1, wherein saidcoagglomerating is carried out by added an electrolyte to thepolymerization system when the polymerization conversion of said vinylmonomer has reached 10 to 50% by weight.